Container preform assembly and method of manufacture

ABSTRACT

A preform assembly for blow molding a container includes a molded plastic preform having an open mouth, a neck surrounding the mouth with an external surface at a first diameter, an external flange at one end of the neck surrounding the mouth, and a preform body integrally molded with the neck at an end of the neck spaced from the flange. The preform body has a second external diameter that is greater than the first diameter of the neck external surface. A circumferentially continuous molded plastic finish ring is externally secured over the external surface of the neck between the flange and the preform body. In the preferred embodiments of the invention, the finish ring is secured to the preform neck by expanding the ring over the flange and then allowing the ring resiliently to shrink onto the external surface of the neck.

[0001] The present invention is directed to preforms for blow moldingplastic containers, and to methods of making such preforms.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] In the manufacture of plastic containers, it is conventional toinjection mold or compression mold a container preform having a body anda finish with one or more external threads. The finish typically ismolded to its final geometry, while the body of the preform issubsequently blow molded to the desired geometry of the container body.The preform may be of monolayer construction, or may be of multilayerconstruction in which one or more intermediate layers in the preformbody may or may not extend into the finish area of the preform. U.S.Pat. Nos. 4,609,516, 4,710,118 and 4,954,376 illustrate injectionmolding of multilayer container preforms.

[0003] Molding the finish portion of the container as part of thepreform presents a number of problems. For example, when the preformsare formed by injection molding, the plastic material typically isinjected into a mold cavity at the closed end of the preform body, sothat the material must flow along the sides of the preform cavity intothe area in which the finish is molded. The finish typically requiresmore accurate and stable dimensioning than the body of the preform,which may limit the cycle time of the molding process. Furthermore, thefinish portion of the preform is of the same material as at least theouter layers of the preform body, which limits the ability to obtain themost desirable characteristics at the finish. When the preform is ofpolyester construction, such as polyethylene terephthalate (PET), thefinish portion of the preform can be wholly or partially crystallized toimprove the operating characteristics of the finish area, particularlyin hot-fill container applications. However, the requirement that thefinish be of the same material as at least the outer layers of thepreform body still limits the design capabilities of preformmanufacture.

[0004] A preform assembly for blow molding a container in accordancewith one aspect of the present invention includes a molded plasticpreform having an open mouth, a neck surrounding the mouth with anexternal surface at a first diameter, an external flange at one end ofthe neck surrounding the mouth, and a preform body integrally moldedwith the neck at an end of the neck spaced from the flange. The preformbody has a second external diameter that is greater than the firstdiameter of the neck external surface. A circumferentially continuousmolded plastic finish ring is externally secured over the externalsurface of the neck between the flange and the preform body. In thepreferred embodiments of the invention, the finish ring is secured tothe preform neck by expanding the ring over the flange and then allowingthe ring resiliently to shrink onto the external surface of the neck.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The invention, together with additional objects, features,advantages and aspects thereof, will be best understood from thefollowing description, the appended claims and the accompanyingdrawings, in which:

[0006]FIG. 1 is perspective view of a preform assembly in accordancewith one exemplary presently preferred embodiment of the invention;

[0007]FIG. 2 is a perspective view of the preform in the assembly ofFIG. 1;

[0008]FIGS. 3 and 4 are perspective views that illustrate sequentialstages of assembly of the preform assembly of FIG. 1; and

[0009]FIG. 5 is a fragmentary sectional view of a portion of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0010]FIG. 1 illustrates a preform assembly 20 in accordance with onepresently preferred embodiment of the invention as including a preform22 and a separate finish ring 24 secured thereto. As best seen in FIG.2, preform 22 includes a body 26 having a closed lower end. (Directionalwords such as “upper” and “lower” are employed by way of description andnot limitation with respect to the upright orientation of the preformand assembly illustrated in the drawings. Directional words such as“radial” and “circumferential” are employed by way of description andnot limitation with respect to the central axis of the preform neck orfinish ring as appropriate.) A neck 28, which typically is cylindrical,integrally extends from the upper end of preform body 26, and a flange30 extends radially outwardly from the open end of neck 28. Neck 28 andflange 30 surround the open mouth 31 of preform 22. Finish ring 24 iscircumferentially continuous, and preferably has one or more externalthreads or thread segments 32. In the illustrated preferred embodimentof the invention, finish ring 24 includes an annular wall 34 from whichthreads 32 project. A tamper-indicating bead 36 extends radiallyoutwardly from wall 34 beneath threads 32, and a capping flange 38extends radially outwardly from wall 34 beneath bead 36. As analternative, capping flange 38 can be molded onto preform neck 28. Theinside diameter of finish ring wall 34 is less than the outside diameterof flange 30, and is less than the outside diameter of preform body 26.

[0011] Finish ring 24 is assembled to preform 22 employing a taperedanvil 40 (FIGS. 3-5). Anvil 40 has a nose 42 sized for close receiptwithin preform mouth 31, and a shoulder 44 for abutting engagement withthe upper surface of flange 30. The upper portion of anvil 40 has atapered outer surface 46, preferably a conical outer surface, having adiameter at ledge 44 equal to or slightly greater than the outsidediameter of flange 30, and an outside diameter at the remote end ofsurface 46 that is less than the inside diameter of finish ring 24.Finish ring 24 is pushed along surface 46 of anvil 40 resiliently toexpand the diameter of the finish ring. When the finish ring is movedpast flange 30, the finish ring resiliently contracts around neck 28 ofpreform 22. The relaxed diameter of ring 24 preferably is such that ring24 is retained by interference fit on neck 28 after expansion over anvil40 followed by contraction onto neck 28. Adhesive or ultrasonic weldingcan also be employed to enhance securement of ring 24 on preform 22. Thefinish and/or preform neck can be provided with suitable means forpreventing rotation of the ring on the neck.

[0012] Preform 22 may be of any suitable plastic construction, such asmonolayer PET or multilayer construction of PET layers alternating withlayers of barrier resin such as ethylene vinyl alcohol (EVOH) or nylon.Preform 22 may be injection molded or compression molded. Likewise,finish ring 24 may be of injection or compression molded plasticconstruction. By providing finish ring 24 separate from preform 22,finish ring 24 may be of any desired material construction, either thesame as or more preferably different from the material construction ofpreform 22. In other words, the material and conditions of fabricationof finish ring 24 may be selected separately from the material andmanufacturing conditions of preform 22 to achieve desired operatingcharacteristics at the finish area of the preform and the finalcontainer. Furthermore, the preform can be molded with thin wallsections without having to accommodate flow of material into a thickerfinish area, which reduces material cost and mold cycle time. Finishring 24 may be of polypropylene (PP) construction, which has sufficientresiliency to expand over anvil 40 and then “snap” or shrink back ontopreform neck 28 and be secured by interference shrink fit on the preformneck. Polyester material, such as PET, PEN or process regrind, can bestretched while warm over anvil 40, and will shrink back onto preformneck 28 as the ring cools.

[0013] There have thus been disclosed a preform assembly and method ofmanufacture that fully satisfy all of the objects and aims previouslyset forth. The invention has been disclosed in conjunction with aexemplary presently preferred embodiment thereof, and a number ofmodifications and variations have been described. Other modificationsand variations will readily suggest themselves to persons of ordinaryskill in the art. The invention is intended to embrace all suchmodifications and variations as fall within the spirit and broad scopeof the appended claims.

1. A preform assembly for blow molding a container, which includes: amolded plastic preform having an open mouth, a neck surrounding saidmouth with an external surface at a first diameter, an external flangeat one end of said neck surrounding said mouth, and a preform bodyintegrally molded with said neck at an end of said neck spaced from saidflange, said body having a second external diameter greater than saidfirst diameter, and a circumferentially continuous molded plastic finishring externally secured to said neck between said flange and said body.2. The preform assembly set forth in claim 1 wherein said finish ring isshrunk fit over said external surface of said neck.
 3. The preformassembly set forth in claim 2 wherein said finish ring is of materialconstruction selected from the group consisting of PP, PET, PEN andprocess regrind.
 4. The preform assembly set forth in claim 1 whereinsaid finish ring has at least one external thread and an externalcapping flange at one axial end of said ring.
 5. The preform assemblyset forth in claim 1 wherein said plastic finish ring is of a materialconstruction selected from the group consisting of: PET, PP, PEN andprocess regrind.
 6. The preform assembly set forth in claim 1 whereinsaid plastic finish ring is of a different material construction fromsaid plastic preform.
 7. A method of making a preform assembly thatincludes the steps of: (a) providing a molded plastic preform that hasan open mouth, a neck surrounding said mouth with an external surface ata first diameter, an external flange at one end of said neck surroundingsaid mouth, and a preform body integrally molded with said neck at anend of said neck spaced from said flange, said body having a secondexternal diameter greater than said first diameter, (b) providing acircumferentially continuous molded plastic finish ring externallysecured to said neck between said flange and said body, and (c)assembling said finish ring to said preform by locating said finish ringover said external surface of said neck and shrinking said ring ontosaid neck such that said ring is secured to said neck by interferenceshrink fit.
 8. The method set forth in claim 7 wherein said step (c) iscarried out by resiliently expanding said ring over said flange and thenallowing said ring to shrink onto said external surface of said neck. 9.The method set forth in claim 8 wherein said step (c) is carried out by:(c1) positioning an anvil over said mouth, said anvil having an outersurface with a diameter at said flange at least equal to that of saidflange, and a diameter spaced from said flange less than the insidediameter of said ring, and (c2) expanding said ring by sliding said ringalong said outer surface until said ring snaps over said flange.